* North Korea says it recently developed advanced H-bomb
* New device's power can reach hundreds of kilotons, it says
* Bomb to be loaded on new ICBM -KCNA (Adds background, details of Kim's visit)
By Jack Kim and Soyoung Kim
SEOUL, Sept 3 (Reuters) - North Korea said on Sunday it has developed a more advanced thermonuclear weapon that possesses "great destructive power" and will be loaded on a new intercontinental ballistic missile (ICBM) that experts believe has the range to hit much of the United States.
The report by North Korea's official KCNA news agency comes amid heightened regional tension following Pyongyang's two tests of ICBM missiles in July that potentially could fly about 10,000 km (6,200 miles), putting many parts of the mainland United States within range.
Under third-generation leader Kim Jong Un, North Korea has been pursuing a nuclear device small and light enough to fit on a long-range ballistic missile, without affecting its range as well as making it capable of surviving re-entry into the Earth's atmosphere.
North Korea "recently succeeded" in making a more advanced hydrogen bomb, the country's official KCNA news agency said.
"The H-bomb, the explosive power of which is adjustable from tens kiloton to hundreds kiloton, is a multi-functional thermonuclear nuke with great destructive power which can be detonated even at high altitudes for super-powerful EMP (electromagnetic pulse) attack according to strategic goals," KCNA said.
"All components of the H-bomb were homemade and all the processes ... were put on the Juche basis, thus enabling the country to produce powerful nuclear weapons as many as it wants," KCNA quoted Kim as saying.
Juche is North Korea's homegrown ruling go-it-alone ideology that is a mix of Marxism and extreme nationalism preached by state founder Kim Il Sung, the current leader's grandfather.
Kim Jong Un, who visited the country's nuclear weapons institute, "watched an H-bomb to be loaded into new ICBM" and "set forth tasks to be fulfilled in the research into nukes," KCNA said.
Pictures released by the agency showed Kim inspecting a silver-colored warhead in the visit accompanied by nuclear scientists, with a concept diagram of its Hwasong-14 long-range ballistic missile seen hanging on the wall.
Tensions on the Korean peninsula have been high since last month when North Korea threatened to launch missiles into the sea near the strategically located U.S. Pacific territory of Guam after U.S. President Donald Trump said Pyongyang would face "fire and fury" if it threatened the United States.